1. Field of the Invention
The present invention relates to a cab of a working machine such as a hydraulic excavator.
2. Description of the Related Art
Generally, a cab of a working machine encloses an operator's seat to protect the same seat. More particularly, the cap is provided with plural support pillars erected around the operator's seat.
There is such a support pillar wherein a closed section is formed by combining a plurality of pressed plates. In this type of support pillar, allowances for welding formed in a longitudinal direction of the constituent plates are brought into surface-contact with each other and are spot-welded intermittently in the longitudinal direction.
In such a support pillar, however, the thickness of each constituent plate cannot be set to a larger value than the thickness which permits the press working. Thus, a limit is encountered in point of the pillar strength. Further, since the constituent plates of this support pillar are joined intermittently in the longitudinal direction, joining strength between plates is weak.
In view of this point there is known a technique which adopts a pipe member as a portion of support pillars, as is disclosed for example in Japanese Patent Laid-Open Nos. 2004-42739 and 2004-42740. According to this technique, since the support pillar formed using the pipe member is of a single pipe member unlike the combination of plates having been subjected to press working, the anxiety about the joining strength is mitigated.
However, in the manufacturing process for the pipe member when adopted, it has so far been difficult to attain required sectional shape and sectional area.
Particularly, in the case of a support pillar as a frame of a working machine, it is desired to set a sectional shape so as to satisfy the strength and shape required for example in accordance with the place where the pillar is to be erected. However, providing the pipe member having a section which satisfies such a condition for each type of a working machine has so far been difficult in fact in point of cost and equipment.